Acute intra-amniotic infection is a major cause of maternal-fetal morbidity and mortality. At present, the pathogenesis of this entity is poorly understood. From a small series, others have suggested that amniotic fluid colony counts greater than 10 to the third power/ml commonly lead to infection while lower counts do not. It has also been speculated that bacterial growth inhibitors, which are frequently found in amniotic fluid, may protect the fetus and mother from infection. The objective of this proposal is to determine the importance of inoculum size and amniotic fluid bacterial growth inhibitors in the development of acute intra-amniotic infection. In a relatively homogenous population, we propose to compare quantitative cultures and frequency of inhibitors in a group with intra-amniotic infection and in an uninfected, matched control group. Quantitative cultures will be performed with standard techniques for aerobic and anaerobic organisms. Inhibitory activity of the amniotic fluid will be assessed by a simple, semi-quantitative method using E. coli and Group B streptococci. This assay will also assess the influence of phosphate and zinc on the inhibitor. With knowledge of the roles of inoculum size and of bacterial inhibitors, it may be possible to predict or prevent some instances of intra-amniotic infection.